Returns the logarithm of the number with respect to an arbitrary base, rounded down.
This method might not be optimized owing to implementation details; `ilog2` can
produce results more efficiently for base 2, and `ilog10` can produce results
more efficiently for base 10.
# Panics
This function will panic if `self` is zero, or if `base` is less than 2.
# Examples
Basic usage:
```
# use ::exint::primitive::*;
# ::exint::uint! {
assert_eq!(5_u24.ilog(5_u24), 1);
# }
```